It is the ultimate badge of honour during the cold snap: knees cruelly exposed to the elements. Postmen at the Royal Mail depot in Hemel Hempstead, Hertfordshire, have continued wearing their summer uniform of shorts as snow has fallen and ice has followed in a knee-trembling battle to see who can tough it out the longest.

The Shorts-Wearing Postman Appreciation Society on Facebook may only boast 19 members but the image of shorts-wearing postmen bravely – or madly – tramping through the snow to deliver Christmas cards and parcels has become one of the most uplifting symbols of stoicism amid the widespread failure of Britain's infrastructure to cope with traditional winter weather.

For John Frew, a postman from Glasgow who now lives in Letchworth, at stake is a round of Christmas drinks – and the respect of his colleagues. "They think I have got an advantage because I come from Scotland, but I have been down here for 22 years and am getting used to this southern-softie weather," he says. "We just decided to do it for a bit of a laugh. As long as I am wrapped up everywhere else, I don't mind wearing shorts. I even wear shorts when I am not working."

Local residents are full of admiration for the shorts-wearing postmen, although Frew admits he has been attracting "some strange looks when I am out delivering the mail, especially when it's been snowing and freezing". Frew has kept his shorts on despite temperatures falling to -8C. But the recent severe weather has whittled the dozen brave postmen who initially set out on the challenge down to just four icy-kneed survivors.

Last winter, postman Jason Urwin from Telford, Shropshire, was hailed as "Britain's bravest postman" for continuing to wear his navy-blue shorts throughout the cold spell. But for Frew, more important than media exposure or masculine pride is that warming round of drinks. "It's a worthy prize," he says.